Yeah, card reader would be my guess too. Before you replace it though, there is one thing you can try. Take out the SD and put a drop or two of isopropyl alcohol (90%+) on the pins, then press the card in and out of the reader several times to try to clean the pins in there.
If that doesn't work: [guide|72242]
Don't worry, replacing the SD slot looks like one of the easiest repairs on this thing